In the prior art, it is known to detect leaks in equipment being tested for leaks (test equipment) by detecting how much of a test gas which is a light gas, such as helium, flows into or out of the test equipment and then into a test port of the leak detection system. The leak detection system contains a filter that passes the light gas and rejects heavier gases. Test gas passed through the filter flows to a gas monitoring instrument, such as a mass spectrometer. The test port is evacuated to a relatively low vacuum by a mechanical fore or roughing pump while the filter and monitoring instrument are evacuated to a higher vacuum, generally by the combination of the forepump and a higher vacuum pump, such as a diffusion pump (which can also serve as the filter). It is also necessary to vent the test equipment and/or monitoring instrument to the atmosphere from time to time. While the test equipment and monitoring instrument are vented, it is desirable to disconnect the pumps from the test equipment and the monitoring instrument, so that the pumps can be maintained in a vacuum state during venting and are not excessively loaded after venting. After venting has been performed, the roughing pump is connected to the test equipment and monitoring instrument to evacuate them to a low vacuum level while the diffusion pump remains in a high vacuum state and no gas is permitted to flow into it. After the test equipment and monitoring instrument have been evacuated to the low vacuum level by the roughing pump, the diffusion pump is connected to the monitoring instrument to reduce the pressure in it to the high vacuum level. If only the test equipment is vented, somewhat the same sequence is followed except that the monitoring instrument remains connected to the diffusion pump at all times, but a flow path between the diffusion pump and both of the roughing pump and vacuum equipment is blocked.
One type of prior art system, as disclosed in Briggs, U.S. Pat. No. 3,690,151, commonly assigned with the present invention, employs a diffusion pump as a filter to pass the light gas to the monitoring instrument to the exclusion of heavier gases, as well as for the usual purpose of evacuating the monitoring instrument. The diffusion pump effectively functions as a filter to enable a significant percentage of the light gas to flow to the monitoring instrument, while virtually preventing the flow of heavy gases, such as water vapor and nitrogen. There is back-diffusion of the light gas through vaporized jets of a diffusion pump fluid, usually an organic oil. The heavy gases, however, cannot back-diffuse through the oil vapor jet as easily. The monitoring instrument is responsive only to the light gas leaking from the test equipment and relatively accurate indications of the amount of light gas leaking from the test equipment are obtained. Commercial equipment utilizing this principle has been extensively marketed under the trademark "CONTRA-FLOW". Further improvements in the design of a leak detection system are disclosed in an application entitled "Counterflow Leak Detector With Cold Trap," Ser. No. 506,737, filed June 22, 1983 and commonly assigned.
Prior art leak detectors utilizing a filter, as described broadly above, or in connection with the "CONTRA-FLOW" type device, have employed several valve assemblies to provide the required isolation between the diffusion pump, roughing pump, test port, filter and/or analyzing instrument. The several valves must be activated in a particular sequence to provide the required isolation during venting of the test equipment and/or the monitoring instrument. The valves must also provide isolation between the diffusion pump and roughing pump as well as the test equipment and monitoring instrument during transitional periods when the test equipment and instrument are being evacuated to the roughing pump vacuum and when the instrument is evacuated to the diffusion pump vaccum. The multiple valve assemblies employed in the prior art are relatively expensive and are subject to being operated in an incorrect sequence. If the sequence is not performed correctly, there is a compromise of the vacuum of the roughing and/or diffusion pump. Of course, if the rough pump and/or diffusion pump vaccum is compromised, a considerable delay occurs before a desired vacuum of these pumps can be reached. A prior solution to this problem is described in my U.S. Pat. No. 4,399,690, which discloses a system using manually operated valves.
An entirely different approach to the proper sequencing of valves is to use solenoids to drive the valves with interconnected electrical controls to power the solenoids. The possibilities of building such a system are limited by the relative crudeness of commercially available solenoid-driven vacuum valves.
Since the leak detection system is often used as a diagnostic instrument for occasional trouble-shooting of various operational systems, it is desirable to provide a leak detection system which is portable and consumes a minimum of power for field use. Each component must be chosen or designed to operate efficiently.
Various gate valves, ball valves and other valves operated by solenoids for use in a vacuum system are known in the prior art. Weight and power efficiency are usually not an important consideration. Thus, to provide an improved electrically driven valve system for a leak detection system, it is necessary to re-think the design of the solenoid-driven vacuum valve.